I think they mean very large amounts.. One that wouldn't be expected to be eaten by a dog.
I do feed PResley about 4 grapes every few days. I have always given her them. Garlic powder i also feed to my girl every now and then in her food. I think it is safe as long as you are not feeding them a bunch or so of grapes or a bunch of cloves of garlic...
Now broccoli.. I gave to Presley long before i read that site and she hated it.. She does like it cooked though! but i don't give her it. She eats plenty of good stuff